It is generally known to provide a pressure bulkhead for enclosing, in a pressure-tight manner, the tail end of the pressurized interior of an aircraft fuselage. The pressure bulkhead includes all structural components that are necessary for achieving an airtight and pressure-tight seal of the pressurized interior of the fuselage, and for taking up and further transmitting into the fuselage structure all of the forces that result from the pressure difference on the two opposite sides of the bulkhead. Generally, two types of bulkhead structures are known in the art. Pressure bulkheads of the first type are embodied as curved, stiffened membrane structures, for example in the form of a semi-spherical cup. Pressure bulkheads of the second type are embodied as a planar, skinned-over grid frame structures.
The choice between these two types of pressure bulkheads is based on the respective prevailing boundary conditions, and especially, for example, the available space, the size of the cross-sectional area that is to be enclosed, and the like. Since the curved form of the first type of pressure bulkhead is advantageous for supporting, transferring and counteracting the arising forces, this type of pressure bulkhead can have a lighter weight and simpler construction. Namely, a membrane structure that is subjected to a pressure supports the resulting loads in directions along its curved surface only in the form of meridian forces and circumferential forces. The circumferential forces are all internal forces within the pressure bulkhead. On the other hand, the meridian forces must be taken up and supported by the surrounding structures of the aircraft fuselage around the edge of the membrane structure. Moreover, the meridian forces of the membrane structure have an outwardly directed force component around the edge of the membrane at the area of the transition or junction with the aircraft fuselage.
A ring frame or circumferential support frame may be provided for taking up such outwardly directed force components, whereby the ring frame is stressed in its circumferential direction due to the forces resulting from the applied pressure. The ring frame simultaneously serves the purpose of compensating for or bridging between the membrane structure and the cross-section of the fuselage, which under some circumstances may deviate from a circular cross-section. Generally, known ring frames embodied as a metal structure have a modified "I" cross-sectional shape. As a result, the ring frame is a significant component, with respect to its weight and the cost and complexity of manufacturing it. For example, the ring frame typically accounts for approximately 40% of the weight of the entire pressure bulkhead, while the membrane structure itself only accounts for approximately 32% of the weight of the total typical pressure bulkhead.
The conventional manufacturing methods for assembling the pressure bulkhead out of a plurality of segment-shaped milled parts made of aluminum or even of titanium are quite complicated and costly. Moreover, the separate steps typically required for manufacturing the pressure bulkhead out of sheet metal components require that the ring frame is riveted to the membrane structure in an additional work step.
The presently known embodiments of pressure bulkheads in the form of curved membrane structures all suffer the problem of an inadequately durable or fatigue resistant connection of the membrane structure to the fuselage structure, as well as the problem of an inadequate corrosion resistance characteristic. The existing or prevailing stiffness transition between the original undisturbed fuselage structure and the structure of the pressure bulkhead is critical with respect to achieving an adequate fatigue strength when the fuselage is subjected to a cyclical interior pressure load. The corrosion characteristics are similarly critical in typical known pressure bulkhead structures. Namely, corrosion inducing substances typically accumulate in the lower region of the relevant cross-sectional area, and these substances regularly lead to corrosion damage of the fuselage shell structure and of the pressure bulkhead itself, even if drainage holes or the like are provided. It is a further difficulty that the respective affected areas of the structures are typically very difficult to access for inspection or maintenance purposes.
German Patent Laying-Open Document 3,844,080 discloses a pressure bulkhead for enclosing and sealing, in a pressure-tight manner, an axial end of an internal pressurized space within the fuselage of a commercial transport aircraft. The forces resulting from the internal pressure in the aircraft are taken up by the bulkhead and transferred into the fuselage structure. The bulkhead has a two part construction, including a network of tension elements such as cables, chains, belts or straps, metal ribs, metal sheet stampings or cut-outs, or the like, for taking up the pressure forces, and a flexible membrane supported by the network for providing the pressure seal. The tension elements of the support network are arranged in meridian and circular directions. The tension elements, such as cables, are connected by cable lugs or the like to the fuselage structure, so that the forces resulting in the support network are transferred in the form of tension or pressure forces into the fuselage. Furthermore, a stiff ring may be provided near the outer perimeter of the main supporting network, while additional cables or the like connect the stiff ring to the fuselage. This publication does not provide any suggestions for improving the fatigue strength of the pressure bulkhead and its connection to the aircraft fuselage.
German Patent Laying-Open Document 3,906,170 discloses a pressure bulkhead for sealing and enclosing the pressurized interior of an aircraft. The disclosed pressure bulkhead comprises a concave curved cup-shaped member of fiber reinforced composite material, which may be a monolithic material of woven or knitted or unidirectional fibers embedded in a resin material, and may include a thicker region of carbon fibers around the rim of the bulkhead. The rim of the bulkhead is connected to the fuselage, for example by rivets. The bulkhead has a shape that is always concave facing the pressurized interior of the aircraft. Namely, the bulkhead, including the cupped or curved member and the rim, has a curvature without any inflection point.